Persist included_in_price attributes in tax_rate spec

This took me 25 minutes to figure out.
Negative tax rate amounts (i.e. refunds) now correctly return negative amounts when they are recomputed
Remove has_available_payment validation which no longer does anything
Order shipping rates by cost ascending

This fixes a problem on the frontend that I saw where they were displaying in indeterminate ordering
[frontend] Group adjustments by their labels in checkout/_summary
Unpenderize Promotion#CreateAdjustment perform + destroy
Create shipment taxes when persisting its cost

Start to detach shipment and line item taxes from within the same method
in Order
Remove update_adjustment callback from LineItem

Doing so give us more liberty to trigger any logic we want between
saving a line item and updating its adjustments. e.g. we can trigger
promotions

Also a line item already receives `ItemAdjustment(line_item).update`
when its quantity is increased by `order.contents.add`. Placing an
update_adjustment in an after_save callback is very likely to generate
more queries than we really need
Recalculate item adjustments in OrderContents `update_cart`

Since LineItem no longer update adjustments through an after_save
callback
Update order total when creating line item taxes

Previously we were running `create_tax_charge` from address transition
and in a separate checkout callback updating all totals. This wraps both
line item taxes creation and the order update total in a single method.
Destroy order shipment in `empty!`
Persist shipment total in OrderUpdater

For some reason we missed that. Realized it after checking shipping
total still displayed a old value when emptying the order
Clear out pending specs from shipment_spec.rb

Remove the spec supposed to ensure shipment adjustment recalculation as
shipment adjustment are not really recalculated so far. They only
created and destroyed along with the shipments.

Needed to pass `to_a` to spec confirming that `shipment.set_up_costs`
would create a tax adjustment, shipment.adjustments.tax always return an
ActiveRecord::Relation